The October 1958 instruction, Sacrae musicae disciplina,
implemented the provisions of the 1955 encyclical and sanctioned the singing of "popular religious songs" at the missa tecta (nos. 13-15).This led to the "four-hymn" pattern of participation: a hymn at the entrance, offertory, communion,
and conclusion.
there was some amusement about the consonance with "ham sandwich"
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